Volume control circuit



May 12, 1942. F. A. POLKINGHORN VOLUME CONTROL CIRCUIT Filed March 29, 1940 miss /Nl/E/vof? F A. POL K/NGHORN Arron/vw Patented May 12, 1942 UNITED STATES PATENT oElcE 2,282,744 VOLUME CONTROL CIRCUIT Frank A. Polkinghorn, Bloomfield, N. J., assignor to Bell Telephone Laboratories, Incorporated, New York, N. Y., a corporation of New York Application March 29, 1940, Serial No. 326,759

(Cl. Z50-20) 6 Claims.

This invention relates to volume control circuitsand particularly to automatic volume control circuits for diversity radio receiving systems.

As is known, in diversity systems either the signal waves received in the several diversity branches are combined to produce the final detector output, or the wave from only the diversity branch having the incoming signal of greatest intensity is selectively supplied to the utilization circuit. Heretofore, in both the combination diversity and the selection diversity systems, it has been customary to regulate or control automatically the intensity of the output current supplied to the utilization circuit in accordance with a combined rectified current obtained from the signals in the several diversity branches. While accurate output intensity regulation is obtainable in the combination diversity system with the volume control circuit arrangement mentioned above, it has been found that satisfactory output volume control is not obtainable with-this arrangement in the selection diversity/system.

It is one object of this invention to secure an output of constant intensity in a selection diversity receiving system.

It is a further object of this invention to regulate the output intensity in a selection diversity in accordance with the intensity of onlyl the selected incoming signal.

According to one embodiment of the invention, in a system arranged for three branch di- 4versity selection operation, each branch including an intermediate frequency amplifier and a volume control rectifier, the rectifier output circuits are each connected through a separate switching rectifier to the same point in each amplifier input` circuit. More particularly, the branch rectifier output circuits are connected through a separate rectifier to the same terminal of a common volume control resistance, whereby the volume control voltage used to control thegain of the intermediate frequency amplifiers in each branch, and the high frequency amplifiers, if any, common to the branches, is derived only from the branchA circuit having the strongest incoming signal. A branch selection system, which does not form part of the invention, is provided to connect selectively only the branch having the strongest incoming signal to the translation device.

'I'he invention will be more fully understood from the following specification taken in conjunction with the drawing on which like reference characters denote elements of similar function.

Referring to the drawing, reference characters A, B and C refer to the individual branch circuits of a three branch diversity receiving system arranged for selection diversity operation.

The separate input terminals of the three quency amplifier, as disclosed in Patent 2,173,858,

N. J. Pierce and F. A. Polkinghorn, September 26, 1939.

Each branch circuit includes an intermediate frequency unit 2 comprising a second intermedi--l ate frequency amplifier Yil, a side-band filter 4, a carrier filter 5, a carrier amplifier 6 and a second detector 1. 'I'he intermediate frequency amplifier 3 comprises an input transformer 8, an output transformer 9, a space discharge tube I0 having a cathode Il, control electrode I2 and an anode I3. Reference numeral I 4 designates a source of anode potential. In addition, each branch circuit includes an automatic volume control rectifier I5, a diversity control amplifier I6 and a selection or voice frequency amplifier I1, the rectifier I5 being connected to the output terminals of the carrier amplifier and the amplifiers `I6 and I 'I to the output of the second detector l. Also, each branch includes a volume control resistance I8 connected to the output circuit of the volume control rectifier I5, a diversity selection rectifier I9 connected to the output of the diversity control amplifier I6 and a blending circuit 2!! comprising resistances 2l and a condenser 22 and included in the` input circuit of amplifier I'l. The blending circuit 20 is in effect a two-terminal network having one terminal connected to the grids and the other terminal connected to the cathodes of tubes 23. More particularly, this network includes three paths, one path comprising condenser 22, anotherpath comprising one of the resistances 2l and the remaining path comprising the other resistance 2| and a grid bias battery. The last-mentioned resistance 2l and associated battery are, as ex`- plained below, either connected together or disconnected, dependent upon the position of the relay armatures in the diversity selection circuit.

Each selection amplifier I1 comprises two tubes I 23 connected in push-pull, an input transformer 24 and an output transformer 25. The output terminals of the three selectionampliers |1 are connected to the common output terminals 26 and a translation device (not illustrated) is connected to the com-mon output terminals 26.

The diversity selection circuit associated with diversity control amplifier I6 and the selection amplier I1 comprises a relay 21 having windings 28 and 29 connected, respectively, across the output terminals of the branch A selection rectifier |9 and branch B selection rectifier I9; a relay 30 having windings 3| and 32 connected, respectively, across the output terminals of the branch B selection rectifier I9 and the branch C selection rectifier I9, and a relay 33 having the windings 34 and 35 connected, respectively, across the output terminals of the branch A selection rectifier I9 and the branch C selection rectifier I9. Each of relays 21, 3D and 33 has an armature 36 connected through conductor 31 to the negative terminal of a grid bias selection battery 38, the positive terminal of which is connected to the ground 39 and the cathodes II of the tubes 23 in the amplifiers I 1. Each of the two contacts 40 of relays 21, 30 and 33 is connected through one of the resistances 2| in the blending circuit 2D to the grids 4| of the tubes 23 in one of the selection amplifiers |1. The characters A, B and C adjacent the contacts 40 and relay windings indicate the manner in which these elements are associated `with the branch circuits. More specifically, one of the contacts 40 of relay 21 is connected to a resistance 2| in the branch A blending circuit 20 and the other contact 4I) of this relay is connected to a resistance 2| of the branch B blending circuit 20. Similarly, the contacts 49 of relay 30 are connected to the resistances 2| in the blending circuits in branches C and B; and the contacts 49 of relay 33 are connected to the resistances 2| in the blending circuits of branches A and C. Relay windings 28 and 34 are connected to the output terminals of the branch A rectifier I9; relay windings 29 and 3| to the branch B rectifier I9, and relay windings 32 and 35 to the branch C rectifier I9.

Referring to the volume control circuit associated with the volume control rectifiers I5, one terminal 42 of each volume control resistance I8 is connected to ground 39 and to one terminal 43 of a common volume control resistance 44. The remaining terminal 45 of each resistance I8 is connected, each through a switching rectifier as explained below, to the other terminal 46 of the common resistance 44. A volume control timing circuit 41 is included between the common resistance 44 and the input or grid circuit of each of the controlled amplifiers 3 in the branches A, B and C and other amplifiers (not illustrated) including the common radio or intermediate frequency amplifiers, if any. In accordance with this invention a separate switching rectifier 49 is included in each branch between the terminal 45 of the branch volume control resistance I8 and terminal 46 of the common volume control resistance 44 whereby, as explained below, the volume control voltage across resistance 44 is obtained only from the branch having the highest incoming signal.

In operation, currents representing a received signal wave, each comprising a single side-band and a reduced carrier, are supplied to the input terminals I of the branches A, B and C, the currents supplied to the three branches each corresponding to a different path in the ether. While conceivably the received wave components may be equal in intensity, ordinarily in practice they differ considerably. Considering each branch unit 2, after amplification in amplifier 3, thev side-band component passes' through the sideband filter 4 to the input circuit of the second detector 1 and the carrier component, after passing through filter 5 is amplified by carrier amplifier 6 and supplied to the second detector 1 and to the branch volume control rectifier I5. Different portions of the second detector output energy are supplied to the input circuits of the diversity control amplifier I6 and voice frequency amplifier I1. Assuming the branch volume control voltages appearing across the resistances IB in the three branches differ from each other, the magnitude of the current through the common volume control resistance 44 is determined solely by the highest branch volume control voltage, since the rectifiers 49 in effect cause the highest branch volume control voltage to oppose or block the other two branch volume control voltages. Stated differently, the rectifiers 49 function as automatic switching devices for impressing across the load impedance or resistance 44 only the greatest of the three independent direct current voltages appearing across the three branch volume control resistances I8. The control Voltage across resistance 44 is then supplied through the time constant circuit 41 to the grid-cathode circuit of the controlled amplifiers in the three branches for controlling the amplication in these tubes, in the manner well known in the art. Thus, as the intensity of the highest incoming signal increases, the voltage across resistance 44 increases and the negative bias voltage supplied to all controlled tubes increases whereby the amplification in these tubes decreases. Similarly, the amplification in all controlled tubes in all branches is increased when the intensity of the greatest branch signal decreases.

Referring now to the branch selection circuit, the rectified output energies of tubes I9 in the three branches are each supplied to two relay windings, the branch A rectified energy being supplied to windings 28 and 34, the branch B rectified energy to windings 29 and 3| and the branch C rectified energy to windings 32 and 35. In a sense, relay 21 functions to compare the intensities of the branch A and B signal waves, relay 3|! the intensities of the branch B and C waves and relay 33 the intensities of the branch A and C waves. Thus, assuming the incoming signals supplied to the input terminals of branches A and C have, respectively, the greatest and smallest intensities, the currents in windings 28 and 34 are stronger respectively than those in windings 29 and 35 and the current in winding 3| is stronger than that in winding 32, whereby the armatures 36 will assume the positions shown. It will be seen that under the assumed conditions, a negative potential from battery 38 is impressed on the grid or control electrode II of the selection amplifier I1 in branch B through the armature 36 and one contact 40 of relay 21 and the same negative potential is also impressed on the control electrode II of the selection amplifier I1 in branch C through the armature 36 and contacts 4|) of relays 30 and 33, whereby these two selection amplifiers are rendered inoperative to convey voice frequency waves. Selection amplifier I1 of branch A remains operative, however, and the energy supplied to the output terminals 26 is obtained entirely from branch A. Also, as previously explained, the amplification in all branches is controlled, under the conditions assumed, only by the carrier energy supplied to branch A. Similarly, if the signal energy incoming to branch B is the strongest, only the branch B signal energy is selected for utilization and it alone controls the amplication, and if the signal energy incoming to branch C is the strongest only the branch C signal energy is delivered to the translation device and the `branch C carrier energy alone controls the amplification in thecontrolled amplifiers in all branches. Thus, the gain in all branches is the same whereby proper comparison and selection is obtained and at the same time, in accordance with the invention, the volume control voltage accurately controls, and maintains constant, the selected output energy.

The blending circuit 2D -functions to minimize, at the moment of switching, the output 26 from one branch selection amplifier l1 to another, the undesired effects due to differences in intensity of the signals received by the selectedr branch and by the previously selected branch.

Although the invention has been explained in connection with a specific embodiment, it is not` to be limited thereto, inasmuch as other apparatus may be satisfactorily employed 'in practicing the invention.

What is claimed is:

l. In combination, a plurality of amplifiers for receiving diierent sets of waves of variable intensity, a separate rectifier connected to the output of each amplifier, a plurality of continuously conductive and independently operative unilateral devices and a common volume control resistance, one set of corresponding output terminals of said rectifiers being connected to the same terminal of said resistance and the other set of corresponding terminals of said rectiers being connected to the other terminal of said resistance each through a -diiferentdevicey and said resistance being entirely included in the input circuit of each amplifier.

2. In combination, a plurality of ampliers having separate input circuits for receiving currents representing received wave components of diierent intensity, said amplifiers having a comincluding an amplier havingan input circuit and an output circuit, the input circuits of said branches being energized with radio waves remon output circuit, means for equally controlling resenting the received current of greatest in' tensity.

3. In combination, a plurality of diversity branches having separate input circuits and each least one gain varying element having an input circuit and a volume control rectifier, and means for utilizing only the strongest rectified output to adjust said elements for equal gains, substantially, and to simultaneously prevent the other rectified outputs from controlling said gains, said means comprising a common volume` control resistance connected in shunt to said rectiers and included entirely in each of said input circuits. Y

5. A radio receiving system for receiving signal waves incoming over diverse ether paths comprising a plurality of diversity branch circuits each comprising at least one intermediate frequency amplier having input and output circuits and a volume control rectier having input and output circuits, the output circuit of each amplier beingconnected to the input circuit of its associated control rectifier,v plurality of switching rectifiers, a common volume control resistance included in the input circuit of said amplifiers, the output circuit of each volume control rectier beingI connected through a difierent switching rectifier to said volume control resistance.

6. A diversity radio receiving system for receiving waves of varying intensity comprising a pluralityof branch input circuits a plurality of amplifiers each having input and output circuits, a plurality of control rectiflers each having input and output circuits, a plurality of.

switching rectifiers, each branch input circuit being connected through a separate amplier to the input circuit of a different control rectier and the output circuits of said control rectiers being connected through a separate switching rectier to the same point in the input circuit of each amplier, a utilization circuit, and means for connecting only the branch circuit having the strongest incoming signal to said output circuit whereby the gain in each of said amplifiers is controlled only in accordance with the variations in the strongest branch input signal and the output voltage is maintained constant.

FRANK A. POLKINGHORN. 

